davies



@eine tates atmt fitte,

GEORGE c. nnvEs, OE DAYTON, OHIO, ASSIGN'OR TO THE DAvIEs l SOEEWy COMPANY, OE THE SAME PLAOE.-

y Letters Ptcnt No. 65,6511, dated June 11, 1867.

nrrnwsMEET 1N WOOD-seams.

TO WHOM ITMAY CONCERN:

Be it knownithat I, GEORGE C. DAVIES, oi' Dayton, Montgomery county, Ohio,`have invented@ certain new and useful improvement in woocbscrews; and I' hereby declare the following to be a full, clear, and exact description thereof, reference being had to the accompanying drawings, making part of this specification.

My invention relates to that class of metallic screws technically known as ,wood-sc'rews, in contradistinction from those employed lcrclusively in metal, and which require, in all cases, a specially prepared nut or threaded socket; and my invention, iu addition to the narrow and incisive thread and the tapering or gimlet point which characterize those of the former class, possesses certain novel and important characteristics which I will now proceed to explain. i p Y Like parts aredesgnated by the same letters throughout the several iigures; the letter A in each iigure designating the complete screw, and the letter B the body thereof, divested of its thread. A, Figure 1, is a profile of ,the preferred type of my invention, A being almoditication of the same, and B an approximative represent-ation of the body ot' A or of A', divested of its thread Figurel 2 shows still another moditicatiomvA and B representingthe screw and body respectively. Figures 3, 4, 5, i, aud 7 are diagrams designed to illustrate approximately the principal pre-existing forms of wood-screws. i i

Wood-screws were originally made with a core ori/central part, C, having a cylindrical body connected to a thick neck, el, whose junction with sailrcore had the form of a more or less abrupt conic frustum, represented at g, figs. 3 to 7 inclusive; the said connecting frustum being formed by bringing the tool used in cutting the thread,l by a rapid approach, nearer to the common axis, the tool being sunk to the full depth of the thread in one 'or two convolutions. This rapidly converging intermediate surface, occupying but a small fraction of the screws length, is believed to be common to all screws' heretofore made. The'cutting tool or chaser, as soon as it had reached a sufficient depth for the thread, was then carried forwardparallel with the axis clear out to the end of the blank from which the screw was to be formed. Such a 'screw is represented theoretically atA, fig. 3..

B representing the central portion or core divested of its thread.

In order to'overcome the objections to the blunt point, the expedient was adopted of making a portion only of the core with parallel sides,'and when the chaser approached the c nd of the blank it was again moved toward the axis, so as toform apoint more or less'tapering, at the same time cutting away a portion of the edgesof the thread with a reduction of its diameter, andalso oi' its pitch` oridistance from thread to threadv as the tool approached the point, (see g's. 4 to 7 inclusive.) Screws so formed are known as gimlet points. Some woodscrews havebeen made by taking out more metal from thereoreA or body of the screw on the upper sid'e of the thread vthan the under side, (see fig. 5, and A, iig. 7,) and in some cases,'such as shown atA, iig. 7, each thread has been formed by a prolongedi'curve or tlutingfextending to the next, so as to avoid any ,distinctive core, (see A', g. 7.)

Screws formed like the above are all objectionable in use, Fig. 3, having the whole length of the threaded part of one diameter, requires a hole tobe bored in the wood the Whole length before it can be driven. In fig. 4 the threaded part is the same as in tig. 3, exceptthe point, which is formed by the cutting tool or Chaser being moved toward the axis of the blank as' it app `roaches the termination thereof; the face ci' the cutting edge of the tool or chaser being'held parallel to the ai is of the blank, so asy to cut the spaces between the threads into a series of steps or offsets, as show-n at n, figs. 4 and '5, the cutter at the same timeshearing off the outer edges of the threads, so as to diminish the pitch or longitudinal distance between the convolution as the tool approached the axis. Points formed in this way are -seldom in thei cent1-e of the core, as may be seen by examining any packageot' screws in the market. Such screws may be driven in to, soft wood without4 a previous hole, but the points not being exactly in the centre, they vare liable to be turned aside by a knot or hard grain rin the wood.

'The screw given in iig-5 diiers from iig. donlyjn the core being cut somewhat deeper above'thaubelow the thread. The screwl shown. in hg. G 'has both thread and body tapered the whole length of the threaded part in the manner of a gimlet, the thread gradually diminishing in depth lto the point or apex of the core. `Screws made on this plan are objectionable from their liability to become loosened by a. slight backward turn, when they may be withdrawn by the ugers. i

All screws` made as above, and they are believed to be the only ones inthe market, have one common defect, namely, the Vconstantwlfability to,V rend asunder. at the point W', where the thread is first brought to depth, or, in other words, where the comparatively bulky and unyiclding'shank or neck abrupt-ly joins or merges in the core proper, and which being always at. or near the place of junction of the t-vvo Vpieces to he united by the screw, is the very part on which the most 'severe strain is concentrated, and which should consequently be the strongest insteadotl being the weakest portion ofthe screw. 1\linetyi\ni per cent. of all the screws that break,lan-d thenumber broken is very large, are broken at this point, while of the screws broken in service nearly all give way at the same' point. Another defect in most pointed screws heretofore made is in having the pitch or distance between consecutive threads gradually diminished as'it approaches the point, while the threads near the shank or neck have the objectionable feature of a broad instead ofsharp and incisive edge. These two defects arise from the manner in which the screws are made, and cannot be avoided in the system of manufacture heretofore employed. The contraction of pitch is a serious defect, for it is evident that after the entrance of such a screw into the wood,

each succeeding convolutionof greaterl pitch in taking clfect, insteadot' being aided by the preceding on'es, m ust bc resisted by them, so that those ot' less pitch must be'forecd through the wood bythe succeeding ones et'l greaterpitch, whereby the wood that should sustain the screw is torn and broken by the unequal strain upon it. AnotherY defectvfound in many wood-scrcws is in having theicorc smaller in the/middle and upper end, and larger near the commencement ot' the point, as shown at b, gf''. This is caused by the yielding or springing of the -blank when acted upon by the cutter inthe process of chasing. When the'tool is new and sharpthis defect is not so apparent, but when dull, which it soon becomes, this enlargement'of the core toward the point is very perceptible. Screws so formed are liable to twist oit` in driving into hard wood, in consequence of the severe strain on'the comparatively contracted portion W. Such screws have also an unsteady hold in ,the wood in consequence of the enlargement ofthe hole at the surface by the bulbous point; and, consequently when two pieces of wood, having their meeting surfaces below the junction' of the thread and shank, are fastened together by such screws they are-subject to lateral motion, in consequence of the'holemade by the bulbous p'ontbeing larger than the core at its base. `4 i V i n In order to overcome all these defects,so very vexatious andwell known to wood-workers generally, a

Y screw has been invented by the undersigned, with apparatus for making it, which eectually obviates all the' above-recited defects and irregularities, and which is represented in" figs. 1 and 2. By an examination of Bytig. 1, representing the core of this screw, it willbe seen that-the core, instead of being made up ota cylin-V der with diverging and converging helical terminations at the shank Vand point respectively, is of conoidal or gradually,l but more and ,more rapidly converging formfor itswhole length from shank to point. It will also be seen by examining A and A that the threads of this screw. at their commencement at the shank, are less than' one-thirdtheir maximum depth, but while remaining of uniform diameter, that they graduallyiincrea'se in depth until within two or three convolutions of thepoint where tliey are the deepest, whence they rapidly diminish to thcpoint, which from my peculiar mode of manufacture, and which I desire to make'the subject of a distinct patent, must always be truly axial or at the exact centre of the core. I do not wish, however, to confine myself strictly to this form of screw.- For some purposes the slight shoulder or oii'set at the junction of the shank and thread may be objectionable; this can be avoided by extending'the core above the thread.' as shown i`n iig. 2. j u v Screws embodying my improvement may1 of'course, be used with either-*the customary co nica-l head, as in the accompanying illustration, or with la head of' semispherical, cylindrical, or other form. Screws made in the shape represented in igs. 1 and 2 possess the following decided advantages over those made in the ordinary modes: first, they can be driven easily into wood with little'or vno previous hole; second, the point being always truly axial, they will always `drive in the direction in which they are started; third, the core being lnrgc ,at the base, and gradually diminished throughout its length toward the point, gives the greatest strength where it is most wanted, namely, at W. This additional strength is fully-fifteen pern cent. over the ordinary merchant. able scr'ewg't'ourth, the threads lbeing the deepest where the woodis firmest, these screws have the greatest possible holding power, awhile their outer edges, to within a few convolutions ot' the point, having a uniform diameter, they will continue their hold upon the wood untilnearly;withdrawntherefrom.

I doA not claim agscrew having a conical core, except when vonstructed with threads extending to the point and Ahaving the 'peculiar characteristics herein specified.` f

I claim herein as new, and of my invention l 1. Making wood-screws with a tapering core from neck to point, with threads of equal pitch and external diameter, but of gradually butmore rapidly increasing depth from the base to near the apex of thesaid core, where they again diminish and die out into a central point. I Y

2. Making wood-screws with a. core tapering from its base to its point, with threads of equal pitch and equal external diameter, but of gradually increasing depth from its base to near the point, where it again diminishes and diesout, in combination with a shank with parallel sides or tapered from about its centre to where it joins' the core, substantiallyV as set` forth.

In testimony of which invent-ion I hereunto set my hand.

eno. o. nerviosos.

Witnesses:

J. O. Dnvrns, GEO. H. KNIGHT. 

